Platinum is, because of its processability, heat resistance, oxidation resistance, corrosion resistance and electrochemical properties, utilized not only for decorative articles but also as various types of industrial materials for circuit contact materials, exhaust gas cleaning catalysts, fuel cell electrode catalysts, gas reforming catalysts, photocatalysts, solar cells and the like. When platinum is used as a catalyst, for example, platinum is carried in a particulate form on a support according to the purpose. Since platinum is an expensive noble metal, for example, an active surface area of platinum is attempted to be increased by using platinum in a nanoparticle form of about 1 to 10 nm in diameter in order to raise the utilization efficiency as a catalyst; and also a carrier is desired to have a high specific surface area.
Platinum nanoparticles are used in such a manner by being carried on various types of carriers, and the utility of platinum catalysts largely varies depending on carriers to be used and carrying means. For example, in a fuel cell catalyst, an electrode material is used in which a carrier to be used is usually a carbon particle having a high current collecting capability and a large specific surface area, and nano-particulated platinum is carried in a highly dispersed state. Also in a photocatalyst, it has been known that a catalytic activity is improved by carrying platinum carried on titanium oxide.
However, for example, carbon carriers oxidatively corrode by long-term operation and repeated voltage amplitudes due to load variations and start-and-stops of batteries. Additionally, platinum nanoparticles carried in a highly dispersed state enlarge their form by repetition of aggregation, and cause reduction of the active surface area and a large decrease of the initial efficiency. Therefore, means are proposed which use, as carriers, nanoparticles of corrosion-resistive metal oxides such as titania and alumina (see Patent Literature 1), silica (see Patent Literature 2) or tungsten (see Patent Literature 3) by compositing these nanoparticles with carbon.